Hey, guys. This has been a really informative discussion. Lots of great opinions, and lots of great facts. I really appreciate you all chiming in here -- there's a lot of knowledge in this community!
So I think I'll continue to work on my playing technique, but also continue to tweak One thing I need to check is which side of the PI circuit the bigger resistor is on! Also, I especially appreciated the input on adjusting the trimmer (thanks, heisthl). This has always been a mystery to me. Maybe it's untrained ears, but it's never seemed to do much on my first amp, and hence I was hesitant to touch it on the second because it was sounding good.
Mark.
"...there are flying v's and then there are the ones shaped like peanuts..." - my son at age 9
markmalin wrote:Hey, guys. This has been a really informative discussion. Lots of great opinions, and lots of great facts. I really appreciate you all chiming in here -- there's a lot of knowledge in this community!
So I think I'll continue to work on my playing technique, but also continue to tweak One thing I need to check is which side of the PI circuit the bigger resistor is on! Also, I especially appreciated the input on adjusting the trimmer (thanks, heisthl). This has always been a mystery to me. Maybe it's untrained ears, but it's never seemed to do much on my first amp, and hence I was hesitant to touch it on the second because it was sounding good.
Mark.
check this layout...there you can see it...
When I adjust the trimmer I also listen to high notes,...for example the G on the high E string in the XV position... When it has that loud PING when you play it you're in the right direction imho.
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markmalin wrote:
...snip...
So I think I'll continue to work on my playing technique, but also continue to tweak One thing I need to check is which side of the PI circuit the bigger resistor is on! Also, I especially appreciated the input on adjusting the trimmer (thanks, heisthl). This has always been a mystery to me. Maybe it's untrained ears, but it's never seemed to do much on my first amp, and hence I was hesitant to touch it on the second because it was sounding good.
Mark.
check this layout...there you can see it...
When I adjust the trimmer I also listen to high notes,...for example the G on the high E string in the XV position... When it has that loud PING when you play it you're in the right direction imho.
Thanks. I've got it right, then. (actually that's the circuit I built but with a slightly larger FB resistor and slightly different values in the power supply string.)
Last night I was tweaking the PI trimmer on the chassis I just built and I could hear the difference, though your comment about playing a G on the high E string is something I'll have to try tonight.
Mark.
"...there are flying v's and then there are the ones shaped like peanuts..." - my son at age 9
Structo wrote:How did you implement the trimmer on the D'Lite?
I'd like to add one to mine but the layout isn't too conducive for it.
Tom, I put one in mine: instead of the lower R resistor, I put in a higher one (200k?) and paralleled a laydown 1M trimmer with that, just glued to the board. It has worked fine so far. Fan of redundancy, I guess...you could just as easily put in a smaller trimmer, but this gives me pretty precise adjustment.
I'm having a hard time visualizing how to install the trimmer there.
Do you have a picture or diagram on how you did it?
Seems like you would have to split the two plate resistors where they join and have each outside leg of the trimmer feed those with the B+ entering the middle leg.
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Structo wrote:How did you implement the trimmer on the D'Lite?
I'd like to add one to mine but the layout isn't too conducive for it.
Tom,
with the two amps I built I put the center connection of the trimmer in the eyelet where the two plate resistors normally connect, then I bent the other two trimmer pins (tabs) up in a u shape and soldered the plate resistors to them. So the resistors span from the pins on the trimmer (in mid air) to their respective eyelets on the bottom of the board. Email me and I can send you a picture of how I did it tonight if you like: mjmalin(at)uwalumni( dot )com
Mark.
"...there are flying v's and then there are the ones shaped like peanuts..." - my son at age 9
Hi guys - I'm relatively new here and about to embark on building a D-Lite based amp, most likely using the 1977 hybrid non HRM as a starting point (Tweaked D-lite?). I've been reading as much as I can on this forum starting from day 1 and reading backwards. Every question I have seems to eventually get answered if I read far enough. I'm truely amazed and humbled by the amount of knowledge and passion embodied by this site.
So as I said above, my questions EVENTUALLY get answered, but it takes a lot of time since the information is so distributed throughout the site and the search capability is rather limited IHMO. It also helps me to make sure I understand what's really going on by bouncing some thoughts off people who have been there before and can validate or correct me. With that, there is an implied "is this correct?" after each one of my comments below...
Anyway, on the subject of "blooming" or "asymmetry" (even order harmonics) it seems as though there are many places where the asymmetries can be introduced, especially on the verge of clipping - the differences between saturation and cutoff in a preamp tubes, PI asymmetry, power amp tube mismatch. Looks to me like the PI is the easiest place to controlably introduce asymmetry if you have a trimmer. To change the preamp characteristics one would need to play around with the operating point moving away from the center towards a hotter or colder point. Swapping different tubes in and out could get expensive.
Has anyone adjusted the PI trimmer with a scope and correlated the waveform with the sound? Maybe some amps have that mojo and some don't because the PI is pretty far away from symmetrical out of the box? Some don't because they are too symmetrical and the trimmer doesn't have enough range to really change the sound? I'm sure the answer will be different depending on whether you want to optimize for a clean tone or not. My ear is happiest with an amp that is on/slightly over the verge of breakup, I use pedals for anything more. The clean channel on my prosonic is too clean, the distortion channel far to overdriven for my taste.
I guess the thing I'm struggling with is that ultimately my ear will have to be the judge, but there is an almost infinite number of combinations and I'm afraid that it's much easier to move away from the mojo than towards it. I'm trying to get an understanding of where the things that have the biggest influence on the sound are and start there, and also use some tools other than just my ear to help point me in the right direction. Sorry for the rambling post but my brain has been on overload since I decided to tackle my own amp build.
Thanks,
Bill
Yes, it can get confusing with all the different ittinerations of these circuits.
If you are going with the D'Lite topology, just follow the tweaked layout and that will definitley get you in the ballpark.
One thing of note, that layout shows a 500K master pot, it should be 1M.
Also on the original Tweaked layout there is a mistake on the power supply board where the center tap from the OT and the wire from the standby switch connect.
It should go to the choke resistor, not the first filter cap.
I have corrected this in this layout.
If you plan on putting the trimmer for the PI on the board you will want to configure the PI plate resistors like #124 is so you can install the trimmer there.
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wjdunham wrote:Has anyone adjusted the PI trimmer with a scope and correlated the waveform with the sound? Maybe some amps have that mojo and some don't because the PI is pretty far away from symmetrical out of the box? Some don't because they are too symmetrical and the trimmer doesn't have enough range to really change the sound? I'm sure the answer will be different depending on whether you want to optimize for a clean tone or not. My ear is happiest with an amp that is on/slightly over the verge of breakup, I use pedals for anything more. The clean channel on my prosonic is too clean, the distortion channel far to overdriven for my taste.
Don't know how helpful this will be, but I spent quite a bit of time trying to figure out a way to set the PI trimmer in my Bluesmaster build. I used a matched tube and put it on a spectrum analyzer with sine wave tones to try and find the 2nd harmonic sweetspot. I did find a position where the 2nd harmonics bumped up a little bit, but felt that the results were inconclusive and the effect was subtle... The trimmer was very very close to the perfect balance setting as well. Ears work best.
Structo wrote:Yes, it can get confusing with all the different ittinerations of these circuits.
If you are going with the D'Lite topology, just follow the tweaked layout and that will definitley get you in the ballpark.
One thing of note, that layout shows a 500K master pot, it should be 1M.
Also on the original Tweaked layout there is a mistake on the power supply board where the center tap from the OT and the wire from the standby switch connect.
It should go to the choke resistor, not the first filter cap.
I have corrected this in this layout.
If you plan on putting the trimmer for the PI on the board you will want to configure the PI plate resistors like #124 is so you can install the trimmer there.
Structo,
Is the feedback resistor (the one on the OT) correct? Should that be 6.2K rather than 4.7K? It's probably up for debate what sounds best, but I'm just curious.
Mark.
"...there are flying v's and then there are the ones shaped like peanuts..." - my son at age 9
One thing I need to check is which side of the PI circuit the bigger resistor is on! Also, I especially appreciated the input on adjusting the trimmer (thanks, heisthl). This has always been a mystery to me. Maybe it's untrained ears, but it's never seemed to do much on my first amp, and hence I was hesitant to touch it on the second because it was sounding good.
